Grain size and clay mineralogy of Late Quaternary sediments on a tectonically active shelf, the southern Sea of Marmara: clues to hydrographic, tectonic and climatic evolution

The clay mineral content and grain size composition of sediments obtained f rom 29 cores (up to 350 cm in length) on the southern Marmara shelves have been analysed in order to determine the effects of climatic, neotectonic an d hydrodynamic changes on the distribution pattern of Holocene sediments in this sea. Grain size data revealed the occurrence of three types of core characterize d respectively by fine-grained (rich in sill and clay), coarse-grained (ric h in sand and gravel) and fine- to coarse-grained sediments. Clay mineral a ssemblages are dominated by smectite (22-86%), illite (11-70%) and kaolinit e (2-46%) with traces of chlorite. The distribution pattern of the clay min erals in most of the cores reveals upward-increasing smectite and decreasin g illite contents, accompanied by an upward increase in crystallinity index for smectite. Analysis of high-resolution seismic profiles and sedimentation rates sugges ts that the coarser-grained sediments are relict deposits. formed under sha llower water-higher energy conditions at some time during the latest Pleist ocene-Early Holocene. With the beginning of marine transgression during the Early Holocene up to the present, deeper water/lower energy conditions hav e prevailed, characterized by finer-grained sedimentation and increased dep osition of smectite with increased crystallinity. Copyright (C) 1999 John W iley & Sons, Ltd.